Patent Application
20130315748
The present application is related to [GE Docket 252833] and [GE Docket 252388], filed concurrently herewith, which are fully incorporated by reference herein and made a part hereof.
The present application relates generally to apparatus, methods and/or systems for cooling the tips of gas turbine rotor blades. More specifically, but not by way of limitation, the present application relates to apparatus, methods and/or systems related to microchannel design and implementation in turbine blade tips.
In a gas turbine engine, it is well known that air is pressurized in a compressor and used to combust a fuel in a combustor to generate a flow of hot combustion gases, whereupon such gases flow downstream through one or more turbines so that energy can be extracted therefrom. In accordance with such a turbine, generally, rows of circumferentially spaced rotor blades extend radially outwardly from a supporting rotor disk. Each blade typically includes a dovetail that permits assembly and disassembly of the blade in a corresponding dovetail slot in the rotor disk, as well as an airfoil that extends radially outwardly from the dovetail.
The airfoil has a generally concave pressure side and generally convex suction side extending axially between corresponding leading and trailing edges and radially between a root and a tip. It will be understood that the blade tip is spaced closely to a radially outer turbine shroud for minimizing leakage therebetween of the combustion gases flowing downstream between the turbine blades. Maximum efficiency of the engine is obtained by minimizing the tip clearance or gap such that leakage is prevented, but this strategy is limited somewhat by the different thermal and mechanical expansion and contraction rates between the rotor blades and the turbine shroud and the motivation to avoid an undesirable scenario of having excessive tip rub against the shroud during operation.
In addition, because turbine blades are bathed in hot combustion gases, effective cooling is required for ensuring a useful part life. Typically, the blade airfoils are hollow and disposed in flow communication with the compressor so that a portion of pressurized air bled therefrom is received for use in cooling the airfoils. Airfoil cooling is quite sophisticated and may be employed using various forms of internal cooling channels and features, as well as cooling holes through the outer walls of the airfoil for discharging the cooling air. Nevertheless, airfoil tips are particularly difficult to cool since they are located directly adjacent to the turbine shroud and are heated by the hot combustion gases that flow through the tip gap. Accordingly, a portion of the air channeled inside the airfoil of the blade is typically discharged through the tip for the cooling thereof.
It will be appreciated that conventional blade tip design includes several different geometries and configurations that are meant to prevent leakage and increase cooling effectiveness. Exemplary patents include: U.S. Pat. No. 5,261,789 to Butts et al.; U.S. Pat. No. 6,179,556 to Bunker; U.S. Pat. No. 6,190,129 to Mayer et al.; and, U.S. Pat. No. 6,059,530 to Lee. Conventional blade tip designs, however, all have certain shortcomings, including a general failure to adequately reduce leakage and/or allow for efficient tip cooling that minimizes the use of efficiency-robbing compressor bypass air. In addition, as discussed in more detail below, conventional blade tip design, particularly those having a “squealer tip” design, have failed to take advantage of or effectively integrate the benefits of microchannel cooling. As a result, an improved turbine blade tip design that increases the overall effectiveness of the coolant directed to this region would be in great demand.
According to one aspect of the invention, the present application describes a turbine rotor blade used in a gas turbine engine, which includes an airfoil having a tip at an outer radial edge. The airfoil includes a pressure sidewall and a suction sidewall that join together at a leading edge and a trailing edge of the airfoil, the pressure sidewall and the suction sidewall extending from a root to the tip. The tip includes a tip plate and, disposed along an periphery of the tip plate, a rail. The rail includes a microchannel connected to a coolant source.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
In an aspect, the combustor 104 uses liquid and/or gas fuel, such as natural gas or a hydrogen rich synthetic gas, to run the engine. For example, fuel nozzles 110 are in fluid communication with an air supply and a fuel supply 112. The fuel nozzles 110 create an air-fuel mixture, and discharge the air-fuel mixture into the combustor 104, thereby causing a combustion that creates a hot pressurized exhaust gas. The combustor 100 directs the hot pressurized gas through a transition piece into a turbine nozzle (or “stage one nozzle”), and other stages of buckets and nozzles causing turbine 106 rotation. The rotation of turbine 106 causes the shaft 108 to rotate, thereby compressing the air as it flows into the compressor 102. In an embodiment, hot gas path components, including, but not limited to, shrouds, diaphragms, nozzles, buckets and transition pieces are located in the turbine 106, where hot gas flow across the components causes creep, oxidation, wear and thermal fatigue of turbine parts. Controlling the temperature of the hot gas path components can reduce distress modes in the components. The efficiency of the gas turbine increases with an increase in firing temperature in the turbine system 100. As the firing temperature increases, the hot gas path components need to be properly cooled to meet service life. Components with improved arrangements for cooling of regions proximate to the hot gas path and methods for making such components are discussed in detail below with reference to
Each rotor blade 115 generally includes a root or dovetail 122 which may have any conventional form, such as an axial dovetail configured for being mounted in a corresponding dovetail slot in the perimeter of the rotor disk 117. A hollow airfoil 124 is integrally joined to dovetail 122 and extends radially or longitudinally outwardly therefrom. The rotor blade 115 also includes an integral platform 126 disposed at the junction of the airfoil 124 and the dovetail 122 for defining a portion of the radially inner flow path for combustion gases 116. It will be appreciated that the rotor blade 115 may be formed in any conventional manner, and is typically a one-piece casting. It will be seen that the airfoil 124 preferably includes a generally concave pressure sidewall 128 and a circumferentially or laterally opposite, generally convex suction sidewall 130 extending axially between opposite leading and trailing edges 132 and 134, respectively. The sidewalls 128 and 130 also extend in the radial direction from the platform 126 to a radially outer blade tip or tip 137.
Due to certain performance advantages, such as reduced leakage flow, blade tips 137 frequently include a tip rail or rail 150. Coinciding with the pressure sidewall 128 and suction sidewall 130, the rail 150 may be described as including a pressure side rail 152 and a suction side rail 153, respectively. Generally, the pressure side rail 152 extends radially outwardly from the tip plate 148 (i.e., forming an angle of approximately 90°, or close thereto, with the tip plate 148) and extends from the leading edge 132 to the trailing edge 134 of the airfoil 124. As illustrated, the path of pressure side rail 152 is adjacent to or near the outer radial edge of the pressure sidewall 128 (i.e., at or near the periphery of the tip plate 148 such that it aligns with the outer radial edge of the pressure sidewall 128). Similarly, as illustrated, the suction side rail 153 extends radially outwardly from the tip plate 148 (i.e., forming an angle of approximately 90° with the tip plate 148) and extends from the leading edge 132 to the trailing edge 134 of the airfoil. The path of suction side rail 153 is adjacent to or near the outer radial edge of the suction sidewall 130 (i.e., at or near the periphery of the tip plate 148 such that it aligns with the outer radial edge of the suction sidewall 130). Both the pressure side rail 152 and the suction side rail 153 may be described as having an inner surface 157 and an outer surface 159.
Formed in this manner, it will be appreciated that the tip rail 150 defines a tip pocket or cavity 155 at the tip 137 of the rotor blade 115. As one of ordinary skill in the art will appreciate, a tip 137 configured in this manner, i.e., one having this type of cavity 155, is often referred to as a “squealer tip” or a tip having a “squealer pocket or cavity.” The height and width of the pressure side rail 152 and/or the suction side rail 153 (and thus the depth of the cavity 155) may be varied depending on best performance and the size of the overall turbine assembly. It will be appreciated that the tip plate 148 forms the floor of the cavity 155 (i.e., the inner radial boundary of the cavity), the tip rail 150 forms the side walls of the cavity 155, and the cavity 155 remains open through an outer radial face, which, once installed within a turbine engine, is bordered closely by a stationary shroud 120 (see
It will be appreciated that, within the airfoil 124, the pressure 128 and suction sidewalls 130 are spaced apart in the circumferential and axial direction over most or the entire radial span of airfoil 124 to define at least one internal airfoil chamber 156 through the airfoil 124. The airfoil chamber 156 generally channels coolant from a connection at the root of the rotor blade through the airfoil 124 so that the airfoil 124 does not overheat during operation via its exposure to the hot gas path. The coolant is typically compressed air bled from the compressor 102, which may be accomplished in a number of conventional ways. The airfoil chamber 156 may have any of a number of configurations, including, for example, serpentine flow channels with various turbulators therein for enhancing cooling air effectiveness, with cooling air being discharged through various holes positioned along the airfoil 124, such as the film cooling outlets 149 that are shown on the tip plate 148. As discussed in more detail below, it will be appreciated that such an airfoil chamber 156 may be configured or used in conjunction with surface cooling channels or microchannels of the present invention via machining or drilling a passage or connector that connects the airfoil chamber 156 to the formed surface cooling channel or microchannel. This may be done in any conventional manner. It will be appreciated that a connector of this type may be sized or configured such that a metered or desired amount of the coolant flows into the microchannel that it supplies. In addition, as discussed in more detail below, the microchannels described herein may be formed such that they intersect an existing coolant outlet (such as a film cooling outlet 149). In this manner, the microchannel may be supplied with a supply of coolant, i.e., the coolant that previously exited the rotor blade at that location is redirected such that it circulates through the microchannel and exits the rotor blade at another location.
As mentioned, one method used to cool certain areas of rotor blades and other hot gas path parts is through the usage of cooling passages formed very near and that run substantially parallel to the surface of the component. Positioned in this way, the coolant is more directly applied to the hottest portions of the component, which increases its cooling efficiency, while also preventing extreme temperatures from extending into the interior of the rotor blade. However, as one of ordinary skill in the art will recognize, these surface cooling passages—which, as stated, are referred to herein as “microchannels”—are difficult to manufacture because of their small cross-sectional flow area as well as how close they must be positioned near the surface. One method by which such microchannels may be fabricated is by casting them in the blade when the blade is formed. With this method, however, it is typically difficult to form the microchannels close enough to the surface of the component, unless very high-cost casting techniques are used. As such, formation of microchannels via casting typically limits the proximity of the microchannels to the surface of the component being cooled, which thereby limits their effectiveness. As such, other methods have been developed by which such microchannels may be formed. These other methods typically include enclosing grooves formed in the surface of the component after the casting of the component is completed, and then enclosing the grooves with some sort cover such that a hollow passageway is formed very near the surface.
One known method for doing this is to use a coating to enclose the grooves formed on the surface of the component. In this case, the formed groove is typically first filled with filler. Then, the coating is applied over the surface of the component, with the filler supporting the coating so that the grooves are enclosed by the coating, but not filled with it. Once the coating dries, the filler may be leached from the channel such that a hollow, enclosed cooling channel or microchannel is created having a desirably position very close to the component's surface. In a similar known method, the groove may be formed with a narrow neck at the surface level of the component. The neck may be narrow enough to prevent the coating from running into the groove at application without the need of first filling the groove with filler. Another known method uses a metal plate to covers the surface of the component after the grooves have been formed. That is, a plate or foil is brazed onto the surface such that the grooves formed on the surface are covered. Another type of microchannel and method for manufacturing microchannels is described in copending patent application GE Docket No. 252833, which, as stated, is incorporated herein. This application describes an improved microchannel configuration as well as an efficient and cost-effective method by which these surface cooling passages may be fabricated. In this case, a shallow channel or groove formed on surface of the component is enclosed with a cover wire/strip that is welded or brazed thereto. The cover wire/strip may be sized such that, when welded/brazed along its edges, the channel is tightly enclosed while remaining hollow through an inner region where coolant is routed.
The following US patent applications and patents describe with particularity ways in which such microchannels or surface cooling passages may be configured and manufactured, and are hereby incorporated in their entirety in the present application: U.S. Pat. No. 7,487,641; U.S. Pat. No. 6,528,118; U.S. Pat. No. 6,461,108; U.S. Pat. No. 7,900,458; and US Pat. App. No. 20020106457. It will be appreciated that, unless stated otherwise, the microchannels described in this application and, particularly, in the appended claims, may be formed via any of the above referenced methods or any other methods or processes known in the relevant arts.
Extending from a position near the base of the rail 150, it will be appreciated that the microchannel 166 may approximately form an angle with the tip plate 148. In certain preferred embodiments, the angle is between 5° and 40°, though other configurations are also possible. Being canted in this manner, it will be appreciated that the microchannel 168 may increase the area of rail 150 it cools. The microchannel 166 may be linear, as illustrated. In alternative embodiments, the microchannel 166 may be curved or slightly curved.
It will be appreciated that
In certain preferred embodiments, a microchannel 166 is defined herein to be an enclosed restricted internal passageway that extends very near and approximately parallel to an exposed outer surface of the rotor blade. In certain preferred embodiments, and as used herein where indicated, a microchannel 166 is a coolant channel that is positioned less than about 0.050 inches from the outer surface of the rotor blade, which, depending on how the microchannel 166 is formed, may correspond to the thickness of the channel cover 168 and any coating that encloses the microchannel 166. More preferably, such a microchannel resides between 0.040 and 0.020 inches from the outer surface of the rotor blade.
In addition, the cross-sectional flow area is typically restricted in such a microchannel, which allows for the formation of numerous microchannels over the surface of a component, and the more efficient usage of coolant. In certain preferred embodiments, and as used herein where indicated, a microchannel 166 is defined as having a cross-sectional flow area of less than about 0.0036 inches2. More preferably, such microchannels have a cross-sectional flow area between about 0.0025 and 0.009 inches2. In certain preferred embodiments, the average height of a microchannel 166 is between about 0.020 and 0.060 inches, and the average width of a microchannel 166 is between about 0.020 and 0.060 inches.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
